Abstract: in order to achieve such dynamic adaptation, we need an infrastructure for automating J2EE application deployment in such an environment. This need is quite evident to anyone who has ever tried deploying a J2EE application even on a single application server, which is a task that involves a great deal of configuration of both the system services and application components.
Key words: j2ee; component; Distributed; Dynamic Deployment;
1 Introduction
In recent years, we have seen a significant growth in component-based enterprise application development. These applications are typically deployed on company Intranets or on the Internet and are characterized by high transaction volume, large numbers of users and wide area access. Traditionally they are deployed in a central location, using server clustering with load balancing (horizontal partitioning) to sustain user load. However, horizontal partitioning has been shown very efficient only in reducing application-related overheads of user-perceived response times, without having much effect on network-induced latencies. Vertical partitioning (e.g., running web tier and business tier in separate VMs) has been used for fault isolation and load balancing but it is sometimes impractical due to significant run-time overheads (even if one would keep the tiers on a fast local-area network) related to heavy use of remote invocations. Recent work [14] in the context of J2EE component based applications has shown viability of vertical partitioning in wide-area networks without incurring the aforementioned overheads. The key conclusions from that study can be summarized as follows:
• Using properly designed applications, vertical distribution across wide-area networks improves user-perceived latencies.
• Wide-area vertical layering requires replication of application components and maintaining consistency between replicas.
• Additional replicas may be deployed dynamically to handle new requests.
• Different replicas may, in fact, be different implementations of the same component based on usage (read-only, read-write).
• New request paths may reuse components from previously deployed paths.



摘要：為了實現(xiàn)廣域網(wǎng)中符合工業(yè)標(biāo)準(zhǔn)基于組件的應(yīng)用程序中動態(tài)的可適應(yīng)性，我們需要一種框架來在這樣的環(huán)境里自動化地配置J2EE 應(yīng)用程序。這種需要對于哪怕在單一的應(yīng)用程序服務(wù)器上嘗試部署J2EE應(yīng)用的人來說也顯而易見，這種任務(wù)設(shè)計到大量的系統(tǒng)服務(wù)和應(yīng)用組件的配置。
關(guān)鍵詞：j2ee；動態(tài)配置；分布式；組件；
1 前言
近幾年，我們已經(jīng)看到基于組件的企業(yè)應(yīng)用開發(fā)的顯著增加。這種應(yīng)用程序通常被部署在公司的內(nèi)部網(wǎng)或者是因特網(wǎng)上，以高事務(wù)容量，大量的用戶和覆蓋范圍廣的訪問為特征，它通常會被部署在中央?yún)^(qū)域，采用服務(wù)器集群來均衡負(fù)載從而支持用戶下載。但是這種平均負(fù)荷的方法被證明只對減少應(yīng)用轉(zhuǎn)發(fā)的用戶可以察覺的反應(yīng)時間有效，而對于減少網(wǎng)絡(luò)方面的延遲作用不大，垂直分割（例如…運行網(wǎng)絡(luò)層和事務(wù)層在不同的虛擬機(jī)）被用于錯誤分離和均衡負(fù)荷，但是它是不符合實際的由于遠(yuǎn)程調(diào)運的大量使用顯著地增加了運行時時間。最近的著作已經(jīng)表明在廣域網(wǎng)中利用垂直負(fù)荷而不引起前面所述的超時問題的可行性。那非研究的主要結(jié)論可以概括如下：
(1) 應(yīng)用合適的應(yīng)用程序，在廣域網(wǎng)中的垂直負(fù)荷可以察覺的延遲。
(2) 廣域垂直層需要復(fù)制應(yīng)用層組件而且需要維持和原組件間的一致性。
(3) 新加的復(fù)制組件可以被動態(tài)配置以滿足新的需要。
(4) 事實上，不同的復(fù)制組件可能會根據(jù)應(yīng)用不同的方式實現(xiàn)相組件。
(5) 新的請求路徑可以復(fù)用先前的組件配置路徑。